Writing instrument base



FIG. 1 is a top, right, side, perspective view of an ornamental designfor a writing instrument base according to the present invention;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a right side elevational view thereof;

FIG. 5 is a left side elevational view thereof; and,

FIG. 6 is a top plan view thereof.

All portions shown in broken lines are for illustrative purposes onlyand form no part of the claimed design.

The ornamental design for a writing instrument base, as shown anddescribed.